A cement composition has been used widely for external wall materials of buildings and structural bodies of construction since it can provide a cement hardened product excellent in strength and durability. Examples of such a cement composition include a cement paste prepared by adding water to cement, a mortar prepared by admixing sand, which is a fine aggregate, therewith, and a concrete prepared by further admixing gravel, which is a coarse aggregate, therewith. In general, in order to improve the air entrainment and fluidity, cement admixtures are added. Recently, their importance tends to be highly regarded and technical innovations have been developed for them.
The functions of the cement admixtures are to assure sufficient dispersing ability for the cement composition even if water content is decreased, retain the fluidity and workability of the cement composition, and improve the durability and strength along with decrease of water as well as to give an excellent cement composition with stable dispersing ability with the lapse of time. In concrete industrial fields today, concrete provided with such functions has been desired. In order to satisfy such requirements, it becomes very important to decrease the unit water quantity and, also, to prevent the decrease of the fluidity.
Among various cement admixtures, especially polycarboxylic acid type cement dispersants are advantageous as compared with other cement dispersants such as naphthalene ones in terms of excellent dispersing property. With respect to such cement dispersants, Japanese Kokai Publication Sho-57-118058 and Hei-09-142905 disclose cement dispersants comprising copolymers prepared by using predetermined unsaturated polyalkylene glycol ether monomers and maleic acid monomers at predetermined ratios.
Further, Japanese Kokai Publication Hei-05-306152 and Hei-05-345647 disclose cement dispersants comprising copolymers prepared by using predetermined unsaturated polyalkylene glycol ether monomers and maleic acid monomers at predetermined ratios, and polycarboxylic acid type cement dispersants in combination.
However, these techniques do not completely solve decrease of dispersing ability with the lapse of time, and there was a room for contrivance to improve the workability of a cement composition in undertaking construction by giving sufficient fluidity to the cement composition. Further, in a high water reducing ratio range required for high strength concrete, the fluidity of the concrete is deteriorated and, especially, the viscosity is increased under high share condition, so that the pump load becomes extremely high at the time of pump transportation and it becomes difficult to carry out pump transportation. Therefore, there was a room for contrivance in order to decrease the viscosity of the concrete composition, and improve the workability.
In particular, in the case under low temperature environments in winter or the like, concrete temperature falls with the atmospheric temperature. Therefore, there are the problems of the remarkable decrease in the workability by high viscosity, of the increase in the additional amount needed by being insufficient initial dispersing ability of the cement dispersants, and of the decrease in productivity by taking long time for mixing. Accordingly, there was a room for contrivance to exhibit sufficient viscosity decreasing ability and initial dispersing ability even under a low temperature environment as well as a high dispersing ability and dispersion retaining ability even in a high water reducing ratio range.
Further, European Patent Publication No. 1179517 discloses cement dispersants comprising a copolymer, as an essential component, including constitutional unit derived from unsaturated (poly)alkylene glycol ether monomer and constitutional unit derived from (meth)acrylic acid (salt), and WO 02/096823 discloses cement admixtures comprising two polymers as essential constituents, namely a polymer (A1) comprising a constituent unit derived from an unsaturated (poly)alkylene glycol ether monomer and a constituent unit derived from an unsaturated monocarboxylic acid monomer, and a polymer (B1) containing an oxyalkylene group or polyoxyalkylene group and carboxyl group. These cement dispersants are capable of exhibiting high dispersing ability even in a slight amount of addition. However, together with the excellent dispersing ability and dispersion retaining ability even in a high water reducing ratio range, there was a room for contrivance to exhibit sufficient viscosity decreasing ability, and to improve the workability in executing cement composition.